Touching the upper-right corner of the screen on the Galaxy S II using one hand, with its 4.27-inch screen, while you're walking down the street looking at Google Maps, is extremely difficult and frustrating. I pulled out my iPhone 4 to do a quick test, and it turns out that when you hold the iPhone in your left hand and articulate your thumb, you can reach almost exactly to the other side of the screen.
His graphic shows this clearly. It makes some sense. And explains why we may not see any larger screen iPhones. Still, people do perfectly fine with big screen phones like the Galaxy S II, so who knows what Apple could do in the future. [dcurtis]